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Thwarting the Prion Protein

Antibodies to the rogue prion protein may one day provide a cure for variant Creutzfeldt-Jacob disease (vCJD), the deadly human counterpart of mad cow disease, according to new research conducted with mice. Experts caution, however, that any such treatment for humans is still years away.

Degenerative brain diseases like mad cow disease (officially known as bovine spongiform encephalopathy, or BSE), scrapie in sheep, and vCJD in humans are thought to be caused by prions, misfolded versions of a normal cellular protein called PrPC. Inside the brain, prions presumably latch onto PrPC molecules on the surface of nerve cells and impose the prion conformation. The sticky prions then clump, which eventually kill neighboring cells and riddle the brain with holes.

Since the tête-à-tête between prion molecules and normal PrPC seems to be crucial for prion replication, molecular immunologist Anthony Williamson of the Scripps Research Institute in La Jolla, California, figured that keeping them physically apart might block the process. So his team produced seven antibodies that bind to various regions of PrPC and added them to a culture of mouse cells infected with prions.

A week later, the number of prion proteins had dwindled in most cultures; in one dish they had vanished altogether. Even if Williamson removed the antibodies, prions did not reemerge for at least 9 weeks. And when the team injected antibody-treated cells into mouse brains, the animals showed no symptoms at all, whereas animals injected with prion-infected, but untreated, cells died after about 160 days. "This is some clear evidence that the cells are actually being purged of prion infectivity," says Williamson--a "pleasant surprise," he adds, because prions had always been deemed very resilient. The study, presented in the 16 August issue of Nature, mirrors a paper by a group from the Imperial College School of Medicine at St. Mary's in London, published in the 31 July issue of the Proceedings of the National Academy of Sciences.

The studies are an interesting step forward, says neuropathologist Adriano Aguzzi of the University Hospital Zürich, but "the really important question is whether or not these antibodies can clear a prion infection in living organisms," he says. "And unfortunately, there's not the least hint of evidence for this yet." Williamson agrees; it may be hard to get the antibodies to the right place in the brain, he admits, but mouse studies to tackle that issue are well under way.